Environmental pollution has received considerable attention due to their harmful effect on human health and living organisms. The industrial progress causes several severe environmental problems by releasing wide range of toxic compound to the environment. Thousands of hazardous waste locations have been produced worldwide consequential from the accumulation of organic pollutants in soil and water over the years. Monitoring of environmental pollution is therefore one of the most important needs for selecting pollution controlling option. Among various pollutants, organic dyes are hazardous and toxic pollutants and have adverse effect on living organisms. Dyes are carcinogenic, hazardous, mutagenic, toxic (cytotoxic and embryo-toxic) to mammals. Thus dyes are risky and unsafe for human health and environment. Because of its high solubility and stability in water, it has been found in freshwater, marine environments and industrial waste waters and is difficult to degrade by traditional techniques.
TiO2 and ZnO have proven their self as a dynamic photocatalyst. However these photocatalyst only encourage photocatalysis upon irradiation by UV light because it absorb only in the UV region of round about 375 nm with the band gap (˜3.2 ev) in UV region. For solar light photocatalysis, a photocatalyst must promote photocatalysis by irradiation with solar light because solar light spectrum consists of 46% of solar light while the UV light is only 5-7% in the solar light spectrum. This least coverage of UV light in the solar spectrum, the high band gap energy (3.2 eV), and fast charge carrier recombination (within nanoseconds) of ZnO confines its extensive application in the solar light spectrum range.
Several researchers have made and used catalysts to remove contaminants using UV light. Dom et al. (2011) synthesized MgFe2O4, ZnFe2O4 and CaFe2O4 by low temperature microwave sintering and applied for the photocatalytic degradation of organic pollutant using solar light. They found high photocatalytic performance of these oxides by degradation of methylene blue in the presence of solar light. Raja et al. (2007) reported a solar photocatalyst based on cobalt oxide and found to be a good solar photocatalyst for the degradation of azo-dye orange II. Wawrzyniak et al. (2006) have synthesized a solar photocatalyst based on TiO2 containing nitrogen and applied for the degradation of azo-dye which completely degraded under solar light. Wang et al. (2008) degraded L-acid up to 83% by using S-doped TiO2 under solar light. Mohapatra and Parida (2011) have synthesized Zn based layered double hydroxide and applied for the degradation and found that layered double hydroxide will be a prominent solar photocatalyst for the degradation of organic chemicals. Zhu et al. (2010) have developed several solar photocatalyst based on Sm3+, Nd3+, Ce3+ and Pr3+ doped titanium-silica and found as good applicants for industrial applications. Zhao et al. (2008) synthesized TiO2 modified solar photocatalyst and reported as good candidate for the photocatalytic degradation of plastic contaminants under solar light. Im et al. (2010) have synthesized hydrogel/TiO2 photocatalyst for the degradation of organic pollutants under solar light. Pelentridou et al. (2009) treated aqueous solutions of the herbicide azimsulfuron with titanium nanocrystalline films under solar light and found photo degradation of herbicide in few hours demonstrated titanium as best candidate for purification of water containing herbicide. However, there is a need for a catalyst that is cheaper and faster to operate for decontamination use.